1. Field of Invention
The present invention related to a method of fabricating a semiconductor device which prevents short channel hump due to the moisture in an insulating interlayer.
2. Discussion of Related Art
As semiconductor devices are highly integrated, techniques of reducing the device isolating area which is so-called field area occupying relatively large area in a semiconductor device have been developed so far.
In a general method of fabricating semiconductor devices, devices are isolated by local oxidation of silicon(hereinafter abbreviated LOCOS) which oxidizes a field area of a semiconductor substrate thermally. Bird""s beaks are formed, when LOCOS is carried out, as oxygens are diffused to the horizontal direction along with a buffer oxide layer. Therefore, active layers are reduced in size to increase device sizes. That""s why various methods of reducing bird""s beak size as well as isolating devices have been developed.
Shallow trench isolation(hereinafter abbreviated STI), which forms a field oxide layer by forming a trench in a field area of a semiconductor substrate and by filling up the trench with insulating substance to isolated devices, is very useful for reducing a chip size and planarizing a surface of the substrate.
FIG. 1A to FIG. 1E show a method of fabricating a semiconductor device according to a related art.
Referring to FIG. 1A, a buffer oxide 13 is formed on a p typed semiconductor substrate 11 by thermal oxidation. A mask layer 15 is formed by depositing silicon nitride on the buffer oxide layer 13 by chemical vapor deposition(hereinafter abbreviated CVD).
A device isolating area and an active area are defined by patterning the mask and buffer oxide layers 15 and 13 selectively to expose a surface of the semiconductor substrate 11 by photolithography. Then, trenches 17 are formed by etching the exposed surface of the semiconductor substrate 11 by anisotropic etch such as reactive ion etching(hereinafter abbreviated RIE) or plasma etch.
Referring to FIG. 1b, silicon oxide is deposited on the mask layer 15 to fill up the trenches 17 by CVD. And, silicon oxide is etched back to expose the mask layer 15 only to remain inside the trenches 17 by chemical mechanical polishing(hereinafter abbreviated CMP) or RIE. In this case, the silicon oxide just remaining inside the trenches 17 becomes a field oxide layer 19 isolating devices.
An active area of the semiconductor substrate 11 is exposed by removing the mask and pad oxide layers 15 and 13 successively by wet etch. In this case, step difference is reduces as the portion of the field oxide layer 19 which is higher than the surface of the substrate 11 is etched away.
Referring to FIG. 1C, a gate 23 is formed by inserting a gate oxide layer 21 in the active area on the semiconductor substrate 11. The gate oxide layer 21 is formed by oxidizing a surface of the semiconductor substrate 11. The gate 23 is formed by depositing polysilicon doped with impurities on the gate oxide layer 21 by CVD then by patterning the polysilicon to expose the semiconductor substrate 11 by photolithography. In this case, the gate 23 is patterned to the direction of the width of a device, which is perpendicular to the length direction of the device as well as the cross section, overlapped with a predetermined portion of the field oxide layer 19.
Lightly doped regions 25 used as an LDD(lightly doped drain) region are formed by implanting n typed impurities with low dose and energy into the semiconductor substrate 11 in use of the gate 23 as a mask.
Referring to FIG. 1D, insulator such as silicon oxide and the like is deposited on the semiconductor substrate 11 to cover the gate 23 by CVD. And, a sidewall spacer 27 is formed at the lateral sides of the gate 23 by etching back the insulator to expose the semiconductor substrate 11.
Heavily doped regions 29 used for source and drain regions overlapped with the lightly doped regions 25 are formed by implanting n typed impurity ions into the semiconductor substrate 11 with heavy dose and energy in use of the gate 23 and sidewall spacer 27 as a mask. In this case, the portion of the semiconductor substrate 11, which is free from being implanted with impurities, under the gate 23 becomes a channel region of a device.
Referring to FIG. 1E, an insulating interlayer 31 covering the gate 23 and sidewall spacer 27 is formed on the semiconductor substrate 11. In this case, the insulating interlayer 31 is formed to improve the planarization of the surface by depositing TEOS(Tetraethyl orthosilicate) by LPCVD(Low Pressure CVD) or PECVD(Plasma Enhanced CVD).
An etch-stop layer 33 is formed by depositing silicon nitride on the insulating interlayer 31 by CVD. A contact hole 35 exposing the heavily doped region 29 is formed by patterning the etch-stop layer 33 and insulating interlayer 31 by photolithography.
In the contact hole 35, a plug connecting a capacitor to the heavily doped region 29 will be formed. The etch-stop layer 33 prevents the insulating interlayer 31 from being etched when polysilicon is patterned to form capacitor electrodes.
As mentioned in the above explanation of the method of fabricating a semiconductor device, planarization of the surface is improved as the insulating interlayer is formed by depositing TEOS by PECVD or LPCVD.
Unfortunately, as LPCVD or PECVD for depositing TEOS is carried out at low temperature, moisture having less evaporating tendency remains inside when the insulating interlayer is formed. Therefore, the moisture fails to diffuse outside but diffuse downward when the etch-stop layer is formed and treated thermally. And, the moisture diffuses into the comers of the gate through the interface between the semiconductor substrate and field oxide, generating positive fixed charge. Thus, stand-by current is increased as breakdown voltage in the lightly doped regions to the direction of device width of an NMOS transistor is lowered.
Accordingly, the present invention is directed to a method of fabricating a semiconductor device that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.
The object of the present invention is to provide a method of fabricating a semiconductor device which prevents stand-by current from increasing due to the breakdown voltage drop in the lightly doped region to the direction of device width.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention.
The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention includes the steps of forming a trench typed field oxide layer defining an active area in a field area of a semiconductor substrate of a first conductive type, forming a gate to the direction of device width wherein a gate oxide layer is inserted between the gate and semiconductor substrate, forming impurity regions in the semiconductor substrate at both sides of the gate by ion implantation with impurities of a second conductive type, forming an insulating interlayer covering the gate on the semiconductor substrate, and removing moisture contained in the insulating interlayer by thermal treatment.
In another aspect, the present invention includes the steps of forming a trench defining an active area on the field area in a semiconductor substrate of a first conductive type, forming a field oxide layer in the trench, forming a gate oxide layer and an electrically-conductive layer, forming a gate long to the direction of device width on the field and active areas by patterning the electrically-conductive and gate oxide layers, forming lightly doped regions by implanting impurity ions of a second conductive type into the semiconductor substrate in use of the gate as a mask, forming a sidewall spacer at the side of the gate, forming heavily doped regions by implanting the impurity ions of the second conductive type into the semiconductor substrate in use of the gate and sidewall spacer as a mask with predetermined dose and energy which is higher than used for forming the lightly doped regions, forming an insulating interlayer covering the gate on the semiconductor substrate, removing moisture contained in the insulating interlayer by thermal treatment, forming an etch-stop layer on the insulating interlayer with insulator of which etch rate is different that of the insulating interlayer, and forming a contact hole exposing the impurity regions by patterning the etch-stop layer and insulating interlayer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.